1. Field of the Invention
The present invention relates to a rotary switch in which particular ones of fixed contacts are made electrically conductive in correspondence with the rotated position of a contact.
2. Description of the Related Art
FIG. 15 shows the structure of a contact of a blower switch of the type in which, for instance, a blower motor for a vehicle (max. 200-Watt level) is directly switched off. In FIG. 15, first to sixth terminals 2 to 7 are fitted on an insulator assembly 1, and first to sixth fixed contacts 2a to 7a are provided on the terminals 2 to 7 at positions located at the front surface of the insulator assembly 1. In this case, the positions of the fixed contacts 2a to 7a are set so as to be at an identical circular position.
A contact 8, which is rotated by an operation knob (not shown), is provided on the insulator assembly 1 in contact therewith. This contact 8 has first to third arm portions 9 to 11 having identical lengths and at identical angular pitches, and the arm portions 9 to 11 are adapted to rotate in correspondence with the operation of the operation knob. First to third movable contacts 9a to 11a are respectively formed on distal ends of the first to third arm portions 9 to 11. These movable contacts 9a to 11a are adapted to come into contact with the respective fixed contacts 2a to 7a as the center of rotation of the contact 8 is urged by a compression coil spring (not shown).
FIG. 16 shows the configuration of a circuit which is connected to the first to sixth terminals 2 to 7. In FIG. 16, the first terminal 2 is connected to the cathode of a battery as the body is grounded. The second terminal 3 is connected to an ignition switch through a coil 12a of a relay 12. The third terminal 4 is connected to the anode of the battery through a series circuit formed by resistors 13 to 15, a blower motor 16, and a contact 12b of the relay 12. The fourth terminal 5 is connected to a common contact point of the resistors 13 and 14, and the fifth terminal 6 is connected to a common contact point of the resistors 14 and 15, and the sixth terminal 7 is directly connected to the blower motor 16.
Accordingly, in the state in which the operation knob is at a position other than the xe2x80x9cOFFxe2x80x9d position, i.e., when the operation knob has been operated to an air supplying position, the relay 12 is turned on in correspondence with the operation of the ignition switch, and one end of the blower motor 16 is connected to the anode of the battery. At the same time, the other end of the blower motor 16 is connected to the cathode of the battery through the resistors 13 to 15 corresponding to the air supplying position. Consequently, a current corresponding to a resistance value flows across the blower motor 16, and the blower motor 16 rotates in correspondence with the magnitude of the current. Therefore, it is possible to supply air to the interior of the vehicle compartment with four-step intensity corresponding to the air supplying position.
However, although there is a demand for further adding a contact to the blower switch to arrange the intensity of air supply in five steps so as to fine adjust the intensity of air supply, or for using the added contact for another function, the above-described blower switch is capable of coping with only up to four steps with the single contact because of the above-described structure of the contact. For this reason, in a case where five-step switching is required, it is necessary to use two contacts. Hence, there are drawbacks in that the structure becomes complex, and that the external size of the blower switch becomes large in size.
The invention has been devised in view of the above-described circumstances, and its object is to provide a rotary switch which is capable of increasing the number of contacts without enlarging the external shape while using a single contact.
In accordance with the invention, there is provided a rotary switch comprising: an insulator provided with a plurality of terminals respectively having fixed contacts; a contact having a plurality of arm portions, movable contacts respectively provided on distal ends of the arm portions being respectively adapted to slide on the fixed contacts as the contact rotates; and urging means for imparting contact forces with respect to the fixed contacts to the movable contacts by urging a center of rotation of the contact, particular ones of the fixed contacts being made electrically conductive in correspondence with a rotated position of the contact, wherein a particular one of the arm portions in the contact is set to be short, and angles between respective ones of the arm portions are set such that the contact forces of the movable contacts with respect to the fixed contacts assume magnitudes corresponding to a load connected to the fixed contacts.
In accordance with the above-described arrangement, when the contact rotates, the movable contacts provided on the distal ends of the arm portions of the contact slide on the fixed contacts, so that particular ones of fixed contacts are made electrically conductive through the contact. At this time, since a particular one of the arm portions in the contact is set to be short, the fixed contacts where the movable contacts are brought into contact can be arranged at concentric positions. Hence, it becomes possible to increase the number of contacts without enlarging the external shape. In this case, since angles between respective ones of the arm portions are set such that the contact forces of the movable contacts with respect to the fixed contacts assume magnitudes corresponding to a load connected to the fixed contacts, no drawback occurs to the energization of the contacts although the contact forces of the movable contacts with respect to the fixed contacts are nonuniform due to the varying lengths of the arm portions.
In the above-described arrangement, an arrangement may be provided such that the fixed contact with which the movable contact with a large contact force is brought into contact is connected to a large-current load, while the fixed contact with which the movable contact with a small contact force is brought into contact is connected to an energizing means for energizing the large-current load.
In accordance with the above-described arrangement, since the fixed contact with which the movable contact with a small contact force is brought into contact is connected to an energizing means for energizing the large-current load which is connected to the fixed contact with which the movable contact with a large contact force is brought into contact, the current flowing across the movable contact with a small contact force and the fixed contact is small. Hence, no drawback occurs to the energization of the contacts even if the contact force of the movable contact with respect to the fixed contact is small.